The Principle Classification and Characteristics of Laser Cutting

1. Principle And Classification of Laser Cutting

● Principle of laser cutting

The laser cutting uses a focused high-power-density beam to work, so that the irradiated material is rapidly melted, vaporized, ablated, or ignited, and the molten material is blown off by a high-speed airflow coaxial with the beam, thereby cutting the workpiece.

When the laser beam interacts with the material, several processes occur. The intense heat generated by the laser beam rapidly raises the temperature of the material, causing it to melt, vaporize, or undergo a chemical reaction. The specific interaction depends on the material properties, such as its absorption coefficient and melting point, as well as the laser parameters, such as power density and pulse duration.

For materials with low melting points, such as plastics, the laser beam can melt the material as it cuts through. The molten material is then blown away by a gas jet, creating a kerf (the cut width). In the case of materials with higher melting points, such as metals, the laser beam vaporizes the material directly, creating a narrow and precise cut.

Gas assist is commonly used in laser cutting to enhance the cutting process. A gas, such as oxygen or nitrogen, is blown through the nozzle of the cutting head onto the material surface. The gas helps to remove the molten or vaporized material from the cut zone, cools down the material, and prevents the occurrence of burrs or dross. The choice of gas depends on the material being cut and the desired cutting quality.

The kerf width, or the width of the cut, is determined by several factors, including the laser power, focal spot size, material thickness, and cutting speed. The kerf width can be controlled by adjusting these parameters to achieve the desired cutting precision. Additionally, laser cutting can result in a phenomenon called taper, where the cut has a slight conical shape. The taper angle depends on the material properties and laser parameters and can be minimized by optimizing the cutting conditions.

●Laser Basics:

A laser (Light Amplification by Stimulated Emission of Radiation) is a device that produces a concentrated beam of coherent light. It consists of three main components: an active medium, an energy source, and an optical resonator. The active medium, which can be a solid, liquid, or gas, emits photons when energized by the energy source. The optical resonator reflects the photons back and forth through the active medium, amplifying and aligning the light waves. This process leads to the formation of a powerful and coherent laser beam.

● Laser cutting classification

There are several types of lasers used in laser cutting machines, including CO2 lasers, Nd:YAG lasers, and fiber lasers. CO2 lasers are the most common type and use a mixture of carbon dioxide, nitrogen, and helium as the active medium. Nd:YAG lasers utilize a solid-state crystal, such as neodymium-doped yttrium aluminum garnet, as the active medium. Fiber lasers, on the other hand, use an optical fiber doped with rare-earth elements as the active medium. Each type of laser has its unique properties and is suitable for specific cutting applications.

1) CO2 lasers

Commonly used for cutting non-metal materials such as wood, plastic, glass, and textiles.Can also cut metals like mild steel, stainless steel, and aluminum with the right setup.

2）Laser vaporization cutting

The workpiece is heated by a high energy density laser beam, the temperature rises rapidly, the boiling point of the material is reached in a very short time, and the material begins to vaporize to form a vapor. These vapors are ejected at a high speed, and a slit is formed in the material while the vapor is ejected. The heat of vaporization of the material is generally large, so a large power and power density is required for laser gasification cutting.

Laser vaporization cutting is often used for cutting very thin metal and non-metallic materials.

3）Laser melting cutting

When the laser is melted and cut, the metal material is melted by laser heating, and then the non-oxidizing gas is sprayed through a nozzle coaxial with the light beam, and the liquid metal is discharged by the strong pressure of the gas to form a slit. Laser melting and cutting does not need to completely vaporize the metal, and the required energy is only 1/10 of the vaporization cutting.

Laser melt cutting is mainly used for the cutting of some non-oxidizable materials or active metals.

4）Laser oxygen cutting

The principle of laser oxygen cutting is similar to oxyacetylene cutting. It uses a laser as a preheating heat source and uses an active gas such as oxygen as a cutting gas. On the one hand, the injected gas acts on the cutting metal to cause an oxidation reaction to release a large amount of heat of oxidation; on the other hand, the molten oxide and the melt are blown out from the reaction zone to form a slit in the metal. Since the oxidation reaction during the cutting process generates a large amount of heat, the energy required for laser oxidation cutting is only 1/2 of the melt cutting, and the cutting speed is much larger than the laser vaporization cutting and the melting cutting.

Laser oxygen cutting is mainly used for carbon steel, titanium steel and heat-treated metal materials such as heat treatment.

5）Laser dicing and control fracture

Laser dicing is to scan the surface of the brittle material with a high-energy density laser, so that the material is evaporated to a small groove by heat, and then a certain pressure is applied, and the brittle material is cracked at the small groove. Lasers for laser scribing are generally Q-switched lasers and CO2 lasers.

Controlling the fracture is a steep temperature distribution generated by laser engraving, which generates local thermal stress in the brittle material, causing the material to be discontinued.

●Laser Cutting Process

The laser cutting process involves several steps. First, the laser beam is generated by the laser source and guided through a series of mirrors and lenses to the cutting head. The cutting head contains focusing optics that concentrate the laser beam into a small spot size. The focused laser beam is then directed onto the material to be cut.

2. Laser Cutting Features

● Advantage

1) Good cutting quality

Laser cutting can achieve better cutting quality due to the small laser spot, high energy density and fast cutting speed.

2) High cutting efficiency

Due to the transmission characteristics of the laser, the laser cutting machine is generally equipped with multiple numerical control worktables, and the entire cutting process can realize numerical control. When operating, just change the NC program, you can apply the cutting of different shapes of parts, you can carry out two-dimensional cutting, and can realize three-dimensional cutting.

3) Fast cutting speed

Laser cutting does not require fixture fixing materials, which saves fixtures and saves auxiliary time for loading and unloading.

4) Non-contact cutting

There is no contact between the torch and the workpiece during laser cutting, and there is no tool wear. To machine parts of different shapes, there is no need to change the "tool", just change the output parameters of the laser. The laser cutting process has low noise, low vibration and no pollution.

● Disadvantage

Laser cutting Due to the limitation of laser power and equipment volume, laser cutting can only cut medium and small thickness plates and tubes, and the cutting speed decreases significantly as the thickness of the workpiece increases.

Laser cutting equipment is expensive and has a one-time investment.